1. Field of the Invention
The present invention relates to a portable electronic apparatus having a body portion and a display portion which is connected to the body portion through a hinge mechanism such that the display portion is folded down and pulled up with respect to the body portion, and particularly to a hinge mechanism which enables the angle of the display portion to be adjusted with constant force.
2. Description of the Prior Art
In a portable personal computer or a portable word processor, a thin display portion provided with a large-sized display screen, such as a liquid crystal display (LCD), is connected to a body portion such that the display is folded over a keyboard of the body portion and pulled up therefrom. To carry the apparatus, the display portion is folded down to provided an attache-case-like appearance, and, to use the same, the display portion is pulled up and positioned behind the keyboard.
A typical example of a conventional portable electronic apparatus is shown in FIGS. 1 and 2. FIG. 1 is a side view showing an open position and a closed position of the conventional portable electronic apparatus, and FIG. 2 is an enlarged side view showing the hinge shaft of the apparatus in FIG. 1.
As shown in FIG. 1, the conventional portable electronic apparatus has a body portion 1 to which a display portion 3 is connected through a hinge portion 4 such that the display portion 3 is folded down and pulled up with respect to the body portion 1. The display portion 3 is journaled to the body portion 1 through a hinge shaft 44 of the hinge portion 4.
As shown in FIG. 1, when the apparatus is not used, the display portion 3 is positioned at "A" to cover a keyboard 2 of the body portion 1, so that the apparatus may provide a compact appearance, easily be stored and carried, and protect the display portion 3 as well as the keyboard 2.
To use the apparatus, an angle of the display portion 3 is properly adjusted through the hinge shaft 44.
It is required that the angle of the display portion 3 is continuously adjusted within the range of angle .theta. from Y to X shown in FIG. 1 to keep the display portion 3 at a selected angle. To achieve such an adjustment, the hinge shaft 44 is pressed, as shown in FIG. 2, by a presser spring 45 with constant force, so that frictional force between the hinge shaft 44 and the presser spring 45 may keep the display portion 3 at the selected angle.
However, according to the conventional portable electronic apparatus with the above-mentioned arrangement, the angle of the display portion 3 is adjusted by utilizing the frictional force which is always constant, between the hinge shaft 44 and the presser spring 45. Therefore, a moment derived from the product of the weight and the position of gravity center of the display portion 3 changes as the angle .theta. varies. Due to this, force to be applied to the display portion 3 to change the angle thereof shall be increased or decreased.
Namely, the moment will be maximized when the display portion 3 takes a horizontal position X, and will be zero when the display portion 3 takes an upright angle Y. Therefore, in adjusting the angle of the display portion 3, an operator shall apply stronger force as the display portion 3 approaches the position Y, and weaker force as the display portion 3 approaches the position X. In this way, the operator is subjected to bothersome work to, reduce or increase his force to be applied to the display portion 3, and, therefore, the commercial value in terms of operability of the apparatus may be reduced.
Further, with the above-mentioned arrangement, the presser spring 45 shall always tighten the hinge shaft 44 with force which is larger than the maximum moment so that its reaction may be applied to a plastic boss 421 of a hinge base 42, to cause the creep and deteriorate durability and reliability of the hinge portion 4.